Useful information about move units

Table of Contents

What is flow units?

Continuity of move equation

Common flow unit metering strategies in open channels

Eyeball methodology

Flow depth (Manning)

Main equipment

Surface Velocity Meters

Transport time meters

Flow unit measurement methods in full tube functions

Venturi meters

Magnetic flowmeter

Turbine flowmeter

Conclusion

What is circulate units?

Flow fee is the amount of fluid that passes by way of a unit of time. In water sources, circulate is often measured in cubic feet per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a variety of other items. The measurement of water resource circulate is necessary for purposes corresponding to system control, billing, design and tons of different applications. There are several methods to measure circulate in a water resource system. This article outlines some of the more frequent strategies of flow measurement and provides some helpful information about move items measurement.
Continuity of circulate equation

For water flowing in a pipe underneath steady-state conditions (i.e., not various with time), continuity means that water flowing into one end of the pipe must flow out of the other finish. This additionally implies that the flow in the pipe is similar at any point along the length of the pipe. The continuity equation can be expressed as

Flow = Velocity * Area

The idea of continuity in regular state situations ends in the product of velocity * space being equal to a continuing at any point in the pipe. This is a helpful principle for making flow measurements, as shown under.
This is an instance of using the continuity equation to calculate flow. Velocity is measured at 10 ft per second and the cross-sectional area of the circulate is measured at 10 sq. toes. Flow fee = 10 ft per second * 10 sq. toes = a hundred cubic toes per second.
Common flow unit metering strategies in open channels

Eyeball technique

It is typically useful to estimate the flow velocity and cross-sectional space by eye and then multiply the flow velocity by the world to acquire the move velocity (continuity equation). A ruler or tape measure can be used to enhance the accuracy of cross-sectional space measurements, and a stopwatch can be used to improve velocity measurements by timing floating particles moving a set distance. The eyeball methodology can be used to estimate move when solely an “order of magnitude” of flow is required or when the move fee is too low to be measured with a circulate meter.
Flow depth (Manning)

When the channel cross-sectional area and channel slope are identified and uniform flow conditions exist, the Manning’s equation can be used to calculate flow by measuring depth only. The Manning’s equation is an empirical equation that describes the relationship between move fee in an open channel beneath uniform flow circumstances and depth, slope and channel friction coefficient (Manning’s n). Uniform move signifies that depth does not range with the size of the conduit or channel. Flow measurements utilizing Manning’s equation for depth aren’t relevant to progressively altering flow circumstances, corresponding to backwater circumstances upstream of a dam or weir.
The depth circulate methodology of flow measurement is extra accurate than the “eyeball” methodology. The primary challenge with depth-only move measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform move circumstances. This technique is commonly used with ultrasonic flow meters to estimate the flow of a river by measuring solely the water level of the river. Often in these causes, the river level/flow relationship is developed with the help of advanced river hydraulic models to account for advanced channel geometry and channel friction conditions.
Main gear

The primary device is used to measure move in open channels, utilizing structures similar to flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be converted to a move price using an equation or rated curve equation.
Primary devices work by forcing the move via a path of crucial depth, for instance at the prime of a weir or on the throat of a flume. In technical phrases, the important depth is outlined as the depth of the minimal specific energy state that ends in a specific discharge. In apply, this minimal state of vitality means that only one flow corresponds to the critical depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is due to this fact referred to as a “primary” system.
Primary gadgets are a really convenient method of flow measurement as a outcome of the depth could be measured from above the circulate without the necessity to insert a sensor in the water. This makes main circulate meters more reliable and easier to take care of. A drawback of main gadgets is that they’ll cause head loss and backwater within the system. Primary units are sometimes considered to be essentially the most correct methodology of measuring open channel flow.
Surface Velocity Meters

An area velocity meter is an open channel move meter that measures circulate by making two separate measurements of depth and velocity. The depth is transformed to a cross-sectional area using the geometry of the pipe or channel. The flow price is then calculated by multiplying the flow space by the velocity utilizing the continuity equation, therefore the name “AV meter”. Velocity is typically measured using a Doppler sensor, which reflects ultrasound waves again from particles within the fluid and uses the Doppler shift in the reflected sound signal to estimate velocity. Some AV meters measure floor velocity optically to estimate velocity.
AV meters are often used to measure open channel flow in sewers as a outcome of the probes are comparatively small and they are often installed in existing sewer pipes without causing important head loss in the pipe. This additionally permits them for use for temporary or short-term move metering functions for sewer research. one disadvantage of AV meters is that the sensor should be installed in the fluid. In sewers, this requires frequent upkeep to scrub the sensor. AV meters are often thought of less accurate than primary move meters because major devices only must measure depth and depth measurements are more accurate than velocity measurements.
Transport time meters

Transport time meters have been developed in the oil trade to accurately measure flow in massive pipelines. They have been used with some success for open channel move in water metering purposes. Transport time meters additionally use ultrasound like Doppler meters, but instead of bouncing the sound waves off particles in the water like Doppler flow meters, they ship ultrasound waves between two sensors separated from each other by a certain distance along the size of the pipe and makes use of the transmission time of the sound waves to calculate the velocity of the water circulate. Because the speed of sound in the water is understood, the pace of the water could be calculated based on the offset in ultrasonic wave transmission time that occurs as a result of pace of the water.
Transmission time meters could be costly relative to Doppler circulate meters due to the many sensors and sophisticated set up involved. They can be more correct due to the capacity to split the move into horizontal cross sections and measure the velocity of each part.
Flow unit measurement strategies in full tube applications

Venturi meters

Venturi flow meters use the Venturi effect to measure circulate in a full or pressurized pipe through the use of the converging section of the pipe to limit the circulate. According to the continuity equation, the cross-sectional space of the converging part is small and subsequently the velocity is greater within the throat. Due to energy conservation and Bernoulli’s precept, greater velocities within the throat lead to a drop in throat strain. The circulate price can then be decided by measuring the strain drop in the convergent section and calculating the flow fee using Bernoulli’s equation. Venturi meters are more widespread in water metering applications because the pressure measurement ports can become clogged in wastewater applications.
Magnetic flowmeter

The electromagnetic circulate meter works by making use of a magnetic area to the fluid passing via the pipe. This causes a small electron potential distinction that could be measured by the electrode sensor (due to Faraday’s law and electromagnetic induction). The magnitude of the electron potential distinction is proportional to the speed of the water, and the continuity equation can then be used to calculate the flow rate.
An advantage of the magnetometer is that the metering part is identical diameter as the adjacent pipe, so the magnetometer causes no extra head loss. For probably pressure gauge 4 นิ้ว ราคา , magnetometers are used for full (pressure) pipe applications, but nowadays open channel magnetometers may additionally be used.
Turbine flowmeter

A turbine circulate meter is a mechanical move meter that uses a rotating turbine in flow to measure the circulate of water in a pipe. The pace of the turbine is proportional to the velocity and the circulate fee can then be calculated using the continuity equation. Turbine flow meters are only used for water applications because of potential problems with wastewater solids collection and clogging generators.
Conclusion

There are many ways to measure move. Each methodology has completely different benefits, disadvantages and accuracy in numerous applications.
It is important to understand the traits of varied move measurement techniques to assist select the best kind of circulate metering for your software or to correctly interpret the move measurements of present circulate meters. Tools like Apure (IoT-based water data analysis) assist to examine measurements collected by move meters and carry out diagnostics to know circulate meter performance and rapidly course of and analyze the information. Contact us for technical or product service support.
More articles on circulate meters:
Mass circulate price vs volumetric move fee

Relation between move and stress

Ultrasonic circulate meter working precept

Difference between flow meter and flow transmitter
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Table of Contents

What is circulate units?

Continuity of flow equation

Common circulate unit metering methods in open channels

Eyeball technique

Flow depth (Manning)

Main equipment

Surface Velocity Meters

Transport time meters

Flow unit measurement strategies in full tube purposes

Venturi meters

Magnetic flowmeter

Turbine flowmeter

Conclusion

What is circulate units?

Flow price is the volume of fluid that passes via a unit of time. In water assets, circulate is usually measured in cubic toes per second (cfs), cubic meters per second (cms), gallons per minute (gpm), or a wide selection of different models. The measurement of water useful resource circulate is important for applications such as system management, billing, design and lots of different functions. There are several methods to measure flow in a water resource system. This article outlines a few of the more widespread methods of flow measurement and offers some helpful details about move models measurement.
Continuity of move equation

For water flowing in a pipe under steady-state situations (i.e., not varying with time), continuity implies that water flowing into one end of the pipe must move out of the other end. This also means that the circulate within the pipe is similar at any point along the size of the pipe. The continuity equation could be expressed as

Flow = Velocity * Area

The concept of continuity in regular state conditions leads to the product of velocity * space being equal to a relentless at any level in the pipe. This is a useful principle for making circulate measurements, as proven beneath.
This is an instance of using the continuity equation to calculate circulate. Velocity is measured at 10 toes per second and the cross-sectional space of the move is measured at 10 square ft. Flow rate = 10 toes per second * 10 square ft = a hundred cubic ft per second.
Common move unit metering strategies in open channels

Eyeball technique

It is sometimes helpful to estimate the flow velocity and cross-sectional area by eye after which multiply the move velocity by the world to acquire the flow velocity (continuity equation). A ruler or tape measure can be used to improve the accuracy of cross-sectional space measurements, and a stopwatch can be utilized to improve velocity measurements by timing floating particles transferring a set distance. The eyeball method can be utilized to estimate flow when solely an “order of magnitude” of flow is required or when the flow fee is too low to be measured with a move meter.
Flow depth (Manning)

When the channel cross-sectional space and channel slope are recognized and uniform circulate circumstances exist, the Manning’s equation can be used to calculate move by measuring depth only. The Manning’s equation is an empirical equation that describes the connection between flow price in an open channel under uniform circulate situations and depth, slope and channel friction coefficient (Manning’s n). Uniform circulate means that depth does not vary with the length of the conduit or channel. Flow measurements using Manning’s equation for depth usually are not relevant to steadily changing circulate circumstances, such as backwater circumstances upstream of a dam or weir.
The depth move technique of flow measurement is more accurate than the “eyeball” method. The primary challenge with depth-only circulate measurements is the potential for inaccurate Manning’s n estimates, cross-sectional areas, and non-uniform move situations. This method is commonly used with ultrasonic move meters to estimate the flow of a river by measuring only the water stage of the river. Often in these causes, the river level/flow relationship is developed with the assistance of complicated river hydraulic fashions to account for complex channel geometry and channel friction circumstances.
Main tools

The primary system is used to measure flow in open channels, using buildings such as flumes, weirs or dams, to measure circulate by measuring depth. The measured depth can then be converted to a move rate using an equation or rated curve equation.
Primary gadgets work by forcing the flow via a path of critical depth, for example on the high of a weir or at the throat of a flume. In technical terms, the crucial depth is defined because the depth of the minimum particular power state that ends in a specific discharge. In practice, this minimal state of power signifies that only one move corresponds to the important depth. Therefore, measuring only the depth produces a measurement of the corresponding flux and is subsequently referred to as a “primary” system.
Primary devices are a very handy technique of circulate measurement as a result of the depth can be measured from above the circulate with out the necessity to insert a sensor within the water. This makes main circulate meters more dependable and simpler to keep up. A drawback of primary units is that they will trigger head loss and backwater within the system. Primary units are often thought of to be the most correct methodology of measuring open channel flow.
Surface Velocity Meters

An area velocity meter is an open channel move meter that measures flow by making two separate measurements of depth and velocity. The depth is transformed to a cross-sectional area utilizing the geometry of the pipe or channel. The flow rate is then calculated by multiplying the move space by the speed utilizing the continuity equation, hence the identify “AV meter”. Velocity is often measured utilizing a Doppler sensor, which displays ultrasound waves back from particles in the fluid and uses the Doppler shift in the mirrored sound signal to estimate velocity. Some AV meters measure floor velocity optically to estimate velocity.
AV meters are often used to measure open channel move in sewers because the probes are relatively small and they can be installed in existing sewer pipes without causing significant head loss in the pipe. This also permits them for use for temporary or short-term move metering applications for sewer studies. one disadvantage of AV meters is that the sensor have to be put in within the fluid. In sewers, this requires frequent maintenance to wash the sensor. AV meters are sometimes thought of less correct than main move meters because major devices solely need to measure depth and depth measurements are more accurate than velocity measurements.
Transport time meters

Transport time meters have been developed in the oil trade to accurately measure move in giant pipelines. They have been used with some success for open channel flow in water metering applications. Transport time meters additionally use ultrasound like Doppler meters, however as a substitute of bouncing the sound waves off particles within the water like Doppler circulate meters, they send ultrasound waves between two sensors separated from each other by a sure distance along the size of the pipe and makes use of the transmission time of the sound waves to calculate the speed of the water circulate. Because the pace of sound within the water is known, the pace of the water may be calculated primarily based on the offset in ultrasonic wave transmission time that happens as a end result of pace of the water.
Transmission time meters could be costly relative to Doppler circulate meters because of the many sensors and sophisticated set up involved. They may be more accurate due to the ability to separate the move into horizontal cross sections and measure the rate of each section.
Flow unit measurement methods in full tube applications

Venturi meters

Venturi flow meters use the Venturi impact to measure flow in a full or pressurized pipe by using the converging section of the pipe to limit the move. According to the continuity equation, the cross-sectional area of the converging part is small and subsequently the speed is higher within the throat. Due to vitality conservation and Bernoulli’s principle, greater velocities within the throat end in a drop in throat stress. The circulate rate can then be decided by measuring the pressure drop within the convergent part and calculating the flow price using Bernoulli’s equation. Venturi meters are more common in water metering applications as a result of the stress measurement ports can become clogged in wastewater functions.
Magnetic flowmeter

The electromagnetic circulate meter works by making use of a magnetic area to the fluid passing by way of the pipe. This causes a small electron potential distinction that could be measured by the electrode sensor (due to Faraday’s legislation and electromagnetic induction). The magnitude of the electron potential distinction is proportional to the rate of the water, and the continuity equation can then be used to calculate the move rate.
An advantage of the magnetometer is that the metering section is identical diameter because the adjacent pipe, so the magnetometer causes no extra head loss. For the most half, magnetometers are used for full (pressure) pipe functions, however nowadays open channel magnetometers can be used.
Turbine flowmeter

A turbine move meter is a mechanical move meter that makes use of a rotating turbine in circulate to measure the flow of water in a pipe. The pace of the turbine is proportional to the speed and the flow fee can then be calculated using the continuity equation. Turbine move meters are solely used for water purposes as a outcome of potential issues with wastewater solids assortment and clogging turbines.
Conclusion

There are many ways to measure flow. Each method has totally different advantages, disadvantages and accuracy in different functions.
It is necessary to grasp the characteristics of varied circulate measurement methods to assist select the right type of flow metering for your software or to properly interpret the move measurements of current move meters. Tools like Apure (IoT-based water knowledge analysis) help to examine measurements collected by move meters and perform diagnostics to know circulate meter performance and rapidly course of and analyze the data. Contact us for technical or product service assist.
More articles on move meters:
Mass flow rate vs volumetric flow fee

Relation between flow and strain

Ultrasonic move meter working precept

Difference between move meter and circulate transmitter

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